Method and apparatus for cast coating paper



Nov. 12, 1963 B. c. GOTTWALD EI'AL 3,110,612

METHOD AND APPARATUS FOR CAST COATING PAPER Filed Dec. 20. 1960 NCOATING RECEIVING G LAYER PAPER DRI DR COATING .4 PAPER) Ezx'xx on l6 Qi ;;;ii;; u W

VA R REC NG COATING ls BA 5 R EIEfiSUR INVENTORS BRUCE C. GOTTWALD 8VAPOR RECEIVING N M. HAIGH BACKING LAYER here to the drum dryer.

United States Patent O 3,110,612 METHOD AND APPARATUS FOR CAST COATENGPAPER Bruce C. Gottwald and John M. Haigh, Henrico County, Va.,assignors to Albemarle Paper Manufac turiug Company, Richmond, Va., acorporauon of Virginia Filed Dec. 20, 1960, Ser. No. 77,083 13 Claims.((31. 117-6 1) This invention relates generally to a method andapparatus for the high speed coating of paper with an extremely smoothsurface. More particularly, this invention is concerned with a processand apparatus for coating a Web of paper with a cast surface or othersmooth surface at a speed heretofore unobtainable.

The manufacturer today, as is well known, utilizes a colorful andattractive pack-aging or wrapping for his product, which is appealing tothe prospective purchaser, for the reason that such eye catchingpackagings are a significant factor in the sale of any individualproduct. This is particularly true when competitive products are oftenside by side on the retail shelf, each vying for the attention of theconsumer. Thus, more attractive Wrappings or packages have been soughtby manufacturers, to sell their product without adding appreciably tothe cost of the product.

One of the most desirable type of packages from the standpoint ofattractiveness is a cast coated paper such as was disclosed in the basicBradner Patent 1,719,166. A paper so produced has a very smooth surfacewhich is the image of the chromium plated highly polished dryer drumused. While the patented apparatus and process has produced a smoothproduct, there are inherent disadvantages which attend such prior meansand method. Among these disadvantages is the fact that the paperproduced was often distorted and spotty, due to the fact that thecoating was forced away from the drum before drying, by reason of theliquid boiling at the surface between the coating and the drum; In anattempt to eliminate this undesirable situation, the temperature of thedrum was maintained below the boiling point of the liquid in thecoating, which in most cases was water. Thus, the temperature of thedrum was limited to a temperature below 212 F.

While the distorted or spotty product was to some extent avoided byreducing the temperature of the drum, it is obvious that the productionrate was considerably reduced because of the resulting slower dryingrate. As a matter of fact, the average speed of prior cast coatingoperations was limited to about 50-80 feet per minute, due to thenecessity of assuring proper drying of the wet coating. Obviously, thisslow production rate greatly increased the cost of the coated paperproduct.

Attempts to raise the temperature of the drum above the boilingtemperature of the liquid in the coating, to speed up the drying andthus the production rate, resulted in the boiling of the liquid and theblowing of the coating away from the drum immediately after its releasefrom the pressure nip. This blowing causes a splitting of the coatingand the distortion mentioned above. In addition, part of the coatingwill adhere to the dryer and part will remain on the paper, One of thereasons for the splitting of the coating is that the usual aqueouscoating, such as starch or starch and clay, has higher adhesiveproperties than cohesive properties while wet. However, the reverse istrue after the coating has dried. Thus, the blowing which occurs beforethe coating surface has dried, will cause the coating at least partiallyto ad- Further use of this dryer with the adhering portions of thecoating on its surface, only compounds the problem.

According to prior practices, to produce the cast effect on the coating,the coating must initially adhere to the dryer surface. This isaccomplished by means of a single pressure roller at the nip in theprior constructions. In order to avoid sticking of the coating to thedrum after the drying, the surface of the dryer was coated with anoleaginous material. This is disclosed in the Montgomery Patent2,568,288. However, the production rate still could not be safely raisedabove approximately feet per minute.

A later attempt to increase the speed of production of a cast coatedpaper is shown in Hart 2,919,205. Although the production rate isincreased by this process to about 200 feet per minute, it requires aspecial gellable coating which must be gelled before the coating iscontacted by the dryer drum. i

Consequently, it is the primary object of this invention to produce amethod and apparatus which will permit the production of a smooth coatedpaper at a high rate of speed.

Another object of this invention is the production of a cast coatedpaper with a dryer drum heated to above the boiling temperature of theliquid coating vehicle.

Another object of this invention is to produce a cast coated paper athigh speed, without permitting the coating to blow from the dryer drum.

Another object of this invention is the provision of method and meansfor receiving and absorbing the vaporizing from the coating to be caston a paper, without permitting the coating to separate from the dryerdrum.

This invention also has for its object the provision of a means andmethod for continuously maintaining the coating against the dryer drumto dry the coating sufiiciently, such that the cohesive strength of thecoating will resist any distortion due to further drying.

An additional object of this invention is to provide a means and methodfor drying and casting a liquid coated paper at a temperature higherthan the boiling temperature of the liquid without the necessity ofusing a pressure sufficient to overcome the vapor pressure of the liquidat the dryer temperature while continuously maintaining the. coatingagainst the casting surface and preventing the separation of the coatingfrom the dryer surface until the coating is sufiiciently dry, wherebythe cohesive strength of the coating will resist any distortion due tofurther drying.

A further and more limited object of this invention is to produce athigh speed a cast coated paper by receiving the vapor from thevaporizing liquid in the coating be- I fore it has an opportunity toseparate the coating from the drum and additionally maintaining thecoating continuously against the dryer drum.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art, from the following descriptionwhen read in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a schematic side elevational view of the present invention;

FIGURE 2 is a schematic side elevational view of another embodiment ofthe present invention showing the use of a soft flexible roller as thepressure means;

FIGURE 3 is a fragmentary sectional View of the area between the dryerdrum and the pressure applying means.

Briefly, this invention comprises a method and apparatus for drying aliquid coating on a paper into a smooth surface such as a cast surfaceat high speed, by the use of a drum heated toa temperature abovethe,boiling point of the liquid in the coating, the blowing of thecoating being prevented by providing a vapor receiving void behind thepaper surface having the coating, and by continuously maintaining thecoating pressed against the dryer drum with a pressure means until thecohesiveness of the coating is such that further drying will not distortthe coating.

It has been discovered that the blowing of the coating away from thesurface of the dryer drum can be avoided by providing a means of escapefor the vaporized liquid in the wet coating rather than reducing thetemperature of the drum. Thus, it is proposed to heat the dryer drum totemperatures as high as 325 F. or even higher, and permit the vapor toescape through the coating and into a vapor receiving void or backinglayer which is pressed against the back of the paper surface having thecoating thereon.

As can be seen, the vapor from the boiling liquid will not force thecoating from the drum surface, but rather, with the proposedconstruction can pass through both the coating and the normally porouspaper surface into the vapor receiving void in back of the papersurface. The only pressures necessary are those that will hold thecoating on the drum surface. The best determination of these pressuresare those that will overcome the resistance offered by the coating, thepaper and the vapor receiver to the passage of the vapor in other wordsthe pressures necessary to hold the coating on the drum are thosesufficient to overcome the vapor pressure of the liquid at the dryingtemperature less the loss in pressure due to the vapor passing throughthe coating, the paper and into the porous backing. These pressures thatmay be around 20 psi. are less than the vapor pressures of the liquid atthe drying temperature and considerably less than the pressuressuggested in the Hart 2,919,205 patent, which are in the neighborhood of300-380 pounds. per linear inch.

In order to adequately dry the coating so that it will not stick to thedryer drum, it is usually sufficient, as

with a starch adhesive, to dry the surface of the coating whereby thecohesiveness of the coating is greater than the adhesiveness to thedryer drum. However, regardless of the amount of drying, it is importantthat pressure be applied continuously to the coating, such as willovercome the resistance of the vapor to flow into the vapor receivinglayer for a long enough time until the cohesiveness of the coating issuch that further drying will not distort the coating. This can only beaccomplished if there is a means for applying continuous pressure to thecoating, thereby forcing it against the drum along a substantial portionof the drum surface. A feature of this invention, therefore, is themethod and means for applying the necessary pressure over a substantialcircumferential portion of the drum for sufficient time to dry thesurface of the coating sufficiently so that the cohesivenessof thecoating is such that further drying of the coating will not distort thecoating.

The apparatus for carrying out this invention is shown in FIGURE 1,wherein the numeral generally designates the high speed apparatus forproviding an ultrasmooth coating C on a web of paper P.

The paper P may be rough kraft type of paper, which is frequently usedfor making cartons for articles that may, for example, be placed on theusual retail grocery or drug shelf. This type of paper has a roughsurface which does not present as as attractive a package as it could ifthe surface were smooth. To provide this smooth surface, the paperbefore entering the apparatus is coated in any conventional manner as bya wet roller and air knife, not shown, with the usual adhesive ormineral-adhesive containing aqueous coating. The mineral may be any ofthe fine particle type, such as calcium carbonate, clay, etc., while theadhesive may be selected fromthe group such as a protein, starch or astarch derivative, such as acetylated, oxidized, chlorinated, enzymeconverted, corn or potato starch, rubber or acrylic latex and polyvinylalcohol, thermosetting plastics, etc.

Conveying roller 12 conducts the paper P with the wet coating C to thenip of the dryer drum 14, which is heated to a temperature which may beas high as 275-325 F. by a convenient means, such as high pressuresteam, within the drum. The drum 14 preferably has the usual 10-12 footdiameter and a highly polished chromium coated surface, which acts as acasting surface in the known manner, but also, it has been found that amachine finishing of the drum will permit the obtaining of a papersurfaced with a smooth coat.

Wrapped around the conveying roller 12 also is the vapor receiving voidor backing layer 16 composed of any relatively thick (approximately inchthick) layer, such as the continuous felt belt shown. The type of feltis that commercially used and known. For the purposes of this invention,any other smooth surfaced continuous belt-like layer may be used, andmay be composed of wool, cotton, fiberglass or like closely knit, wovenor pressed material. The drum 18 is a dryer roll for the felt, andincreases the water removing capacity of the apparatus.

As is clearly shown in FIGURE 1, the layer 16 is urged against the drum14 around a substantial portion of the circumference of the drum. Bymeans of this feature of the invention, sufficient drying time isachieved. This wrapping which may be up to 270 around the drum, butgenerally at least 5 is accomplished by means of the adjustabletensioning roller 20 having suitable jack means, such as shown at 22.Due to the fact that the layer 16, when made of wool felt for instance,does not have sufilcient tensile strength to withstand even the reducedpressures that can be used in this invention, a pressure means such asthe flexible pressure belt 24 may be utilized. It should be understood,however, that if the vapor receiving layer 16 were strong enough toapply the needed pressure and also capable of absorbing the vapor fromthe coating, the flexible pressure belt 24 would not be necessary. Thebelt 24 may be made of any flexible material that is smooth, such as arubber or plasticv material, or evenmay be constructed of wire that may,for example, be of the woven type. The belts may also be porous ornonporous. However, the use of a porous pressure belt provides anunlimited void or vapor receiving volume, inasmuch as the vapor can passout of the layer 16 through the pores or openings that exist in theporous belt.

It has been found that the amount of void or vapor receiving volumenecessary is dependent upon the amount of vapor generated by the wetcoating, and upon the type of coating. For instance, with a coating thatsets quickly and sufiiciently at the surface, so that its cohesivenessexceeds its :adhesiveness to the dryer drum, the subsequent flashing ofthe remaining liquid in the coating or paper will not afiect the smoothsurface. In such an instance, there is no need for a large enough volumeof void space to receive the additional vapor flashed from the coatingafter the initial drying, but only that which evolved while the coatingpassed through this initial drying.

ininstances where a relatively low coat weight is used, for example, /25pounds per ream, as in the case of an unpigmented coating such asstarch, there of course, would be less need for as great a vaporreceiving void in this [low liquid containing wet coating, as in thecase of a heavier pigmented coating havin a weight range of 12-20 poundsper ream, which would normally contain a greater amount of liquid.Therefore, the layer 16 may be considerably thinner, in the range of 4inch in thickness. It is also possible to omit the use of the layer 16entirely, when the low weight coating is placed upon a porous bulky lowdensity paper board having a density of up toabout 10 pounds per reamper mil. In such a case, the void volume presented by the board behindthe paper surface upon which the low weight coating is placed, can besufiicient to receive all the vapor evolved while the paper ispressurized against the dryer drum. The paper board behind the papersurface, therefore, acts as'the equivalent of the backing layer 16, toabsorb the relatively small amount of liquid vaporized from the wetcoating. It is emphasized that the omission of the layer 16 is onlypermitted during the practice of this invention when 1) the coating isunpigmented, (2) of a solids coating weight less than 5 pounds per reamapplied at not less than 20% solids, (3) placed upon a paper boardhaving a density of up to about pounds per ream per mil, and a minimumthickness of 5 mils.

As best shown in FIGURE 1, there is provided at the nip N a pressureroller 26, which has pressure adjusting means 28 which is similar tomeans 26 on roller 20". The purpose of roller 26 is to form anaccurately defined nip, wherein the coated paper enters the niptangential to the dryer drum surface. The pressure need not be in excessof the pressure applied by the pressure belt 24 throughout its wraparound the drum 14.

In FIGURE 3, there is shown the usual practice of the invention, inwhich the paper P has a coating C backed up by a vapor receiving void orlayer 16, all of which are continuously pressed by the pressure belt 24against the dryer drum 14, heated up as high as 325 F. As previouslystated, the pressure need only be sufficien-t to overcome the resistanceof the passage of the vapor through the coating of the paper and intothe layer 16.

Instead of using the pressure belt 24, as shown in FIGURE 1, thenecessary pressure may be applied by means of a soft rubber roller 30rotating about an axis 32. The roller must be soft enough to cover asubstantial area of the dryer drum, considerably in excess of thecontact that would be provided with the normally used pressure roller.Such a roller can be inflated with air and pressed against the drum toachieve the desired pressure. In order to maintain the pressure of thecoating against the drum for sufiicient time to dry the coating, and yetretain the desired production rate, less pressure can be used to inflatethe roller 30. Thus, there will be a greater pressured wrap of the paperaround the drum.

By utilization of the teaching of this invention, speeds of productionas high as 400 feet per minute have been reached on only a 6 footdiameter dryer and a satisfactory product obtained. With a larger drumdiameter, considerably higher speeds are possible.

The wrapping of the pressure means about the dryer drum, as stated, isto afiord sulficient drying time for the coated paper between thepressure means and the drum. It should be clear that if a smaller drumthan the usual 10-12 feet diameter drums is used, a greater wrapping interms of degrees of wrap must be accomplished to achieve the necessarypressurized drying. Conversely, if a larger drum is used, less degreesof wrapping are necessary.

The following examples illustrate the present invention, and are not tobe considered as limiting the scope of the invention:

' Examples (1) Base stock1 sheet of uncalendered board, density7#/ream/mil, weight 126 lbs/ream, 18 mil thickness, 60% kraft, 40%groundwood.

Coatin-g20 lbs/ream, composed of 100 parts clay, 18 parts protein andwater to make 55% solids.

Dryer temperature-300 F.

Belt pressure33 p.s.i.g., applied continuously over entire sheet.

Felt thickness% inch.

Dryer surfaceChrome plated mirror finish.-

Results: Paper had very smooth finish and high gloss characteristic ofcast coatings.

Base stock1 sheet of uncalendetred board, density 7#/ream/mil, weight126 lbs/ream, 1-8 mil thickness, 60% kraft, 40% groundwood.

Ooating2(l lbs/ream, composed of 100 parts clay, 18 parts protein andwater to make 55% solids.

Dryer temperature35 0 F.

Belt pressure60 p.s.i.g., applied continuously over entire sheet.

'Felt thicknessinch.

Dryer surfaceChrorn'e plated mirror finish.

Results: Paper had very smooth finish and high gloss characteristic ofcast coatings.

Base stock-l sheet uncalenedered board, density 7#/ream/mil, weight 200lbs/ream, 28 mil thickness, 60% kraft, 40% groundwood.

-Coating2 lbs/ream, oxidized starch from 20% solids aqueous solution-Temperature-300 F.

Pressure-33 p.s.i.g.

Felt-None.

Dryer surface-Chrome plated mirror finish.

Results: Paper had very smooth finish and high gloss characteristic ofcast coatings.

Base stock-Calendered board, density 11#/ream/ mil, weight 250 lbs/ream,23 mil thickness, kraft.

Coating20 lbs/ream; solids composed of 100 parts Another run with aboard of density 10#/ream/mil was made under identical conditions asExample #5, with satisfactory results. This would seem to substantiatethe position that for the lower density board used in Example #5, ahigher temperature or lower pressure is possible if the felt wereretained, or the felt could be eliminated entirely, because the lessdense board would have sufiicient void space to receive the releasedvapor.

As used herein, the term ream refers to 500 sheets of paper, each sheetbeing 24 inches by 36 inches.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations, and modifications of the presentinvention which come within the province of those skilled in the art.However, it is intended that all such variations not departing from thespirit of the invention, be considered as within the scope thereof aslimited solely by the appended claims.

What is claimed-is:

1. The method of cast coating paper and the like corn prising coating apaper web surface with a hardenable liquid coating containing a volatileliquid and an adhesive which coating is conformable to a smooth formingsurface, pressing said coating paper surface with a continuous pressingsurface against a smooth forming surface heated to a temperaturesuiiicient to boil said liquid and under a pressure sufiicient tocontinuously maintain said coating against said smooth forming surface,maintaining a vapor receiving web between the coated paper sur-.

face and said pressing surface, continuously maintaining said pressurefor a sufficient time until sufficient volatile liquid has beenvaporized and been driven from the surface of the coating. whereby thecohesive strength of the coating will resist any distortion due tofurther drying.

2. The method of cast coating paper and the like comprising coating apaper web surface with a hardenable liquid coating containing a volatileliquid and an adhesive which coating is conformable to a smooth formingsurface, pressing said coating paper surface with a continuous pressingsurface against a chromium plated drum having a smooth forming surfaceheated to a temperature suiiicient to vaporize said liquid, saidtemperature being above the boiling temperature of the liquid, saidpressing being at a pressure sufficient to continuously maintain saidcoating against said smooth forming surface, maintaining a vaporreceiving web between the coated paper surface and said pressingsurface, continuously maintaining said pressure for a sufficient timeuntil sufficient volatile liquid has-been vaporized and been driven fromthe surface of the coating whereby the cohesive strength of the coatingwill resist any distortion due to further drying.

3. The method of cast coating paper and the like comprising coating apaper web surface with a vhardenable liquid coating containing avolatile liquid and an adhesive which coating is conformable to a smoothforming surface, pressing said coated paper surface with a continuouspressing surface against a chromium plated drum having a smooth formingsurface heated to a temperature sufiicient to vaporize said liquid, saidtemperature eing above the boiling temperature of the liquid, saidpressing being at a pressure sufficient to continuously maintain saidcoating against said smooth forming surface, maintaining a vaporreceiving void formed by a felt belt between the coated paper surfaceand said pressing surface, continuously maintaining said pressure for asuflicient time until sufficient volatile liquid has been vaporized andbeen driven from the surface of the coating whereby the cohesivestrength of the coating Will resist any distortion due to furtherdrying.

4. The method of cast coating a rough thick paper board having a papersurface and a porous substantially thick vapor receiving backing with ahardenable liquid coating containing a volatile liquid which coatingisconformable to a smooth forming surface, pressing said coated papersurface with a continuous pressing surface against asmooth formingsurface heated to a temperature sufiicient to boil said liquid and undera pressure sufficient to continuously maintain said coating against saidsmooth forming surface, continuously maintaining said pressure for asufiicient time until sufiicient volatile liquid has been vaporized andbeen driven from the surface of the coating whereby the cohesivestrength of the coating will resist any distortion due to furtherdrying.

5. The method of cast coating paper and the like comprising coating apaper web surface with a hardenable liquid coating containing anadhesive selected from the group consisting of starch, a starchderivative polyvinyl alcohol, rubber and acrylic latex, and a proteinand a volatile liquid which coating is conformable to a smooth formingsurface, pressing said coated paper surface with a continuous pressingsurface against a smooth forming surface heated to a temperaturesufficient to boil said liquid and under a pressure sufficient tocontinuously maintain said coating against said smooth forming surface,main taining a vapor receiving Web between the coated paper surface andsaid pressing surface, continuously maintaining said pressure for asufficient time until sufficient volatile liquid has been vaporized andbeen driven fromthe surface of the coating whereby the cohesive strengthof the coating will resist any distortion due to further drying.

6. The method of cast coating paper and the like comprising coating apaper web surface with a hardenablc liquid coating containing a pigmentand an adhesive selected from the group consisting of starch, a starchderivative polyvinyl alcohol, rubber and acrylic latex and a protein,and a volatile liquid, said volatile liquid being water, which coatingis conformable to a smooth forming surface, pressing said coated papersurface with a continuous pressing surface against a smooth formingsurface heated to a temperature sufficient to boil said liquid, saidpressing being at a pressure sufficient to continuously maintain saidcoating against said smooth forming surface, maintaining a vaporreceiving web between the coated paper surface and said pressingsurface, continuously maintaining said pressure for a sufficient timeuntil sufficient volatile \ilqllld has been vaporized and been drivenfrom the surface of the coating whereby the cohesive strength of thecoating will resist any distortion due to further drying.

7. The method of cast coating paper and the like comprising coating apaper web surface with a hardenable liquid coating containing a volatileliquid which coating is conformable to a smooth forming surface,pressing said coated paper surface with a continuous pressing surfaceagainst a smooth forming surface heated to a temperature sufficient tovaporize said liquid, said temperature being above the boilingtemperature of the liquid, said pressing being at a pressure less thanthe vapor pressure of the liquid being vaporized, said pressure beingsufficient to continuously maintain said coating against said smoothforming surface, maintaining a vapor receiving web between the coatedpaper surface and said pressing surface, continuously maintaining saidpressure for a suflicient time until suflicient volatile liquid has beenvaporized and been driven from the surf-ace of the coating whereby thecohesive strength of the coating will resist any distortion due tofurther drying.

8. The apparatus of claim 9, wherein said pressure member for applyingpressure includes a drum conforming roller which conforms to the shapeof the drum through a substantial circumferential arc of said drum.

9. Apparatus for casting a wet coating on a paper wherein the coatingincludes solids and a liquid comprising; rotatable casting drum having asmooth polished surface heated to a temperature in excess of the boilingtem- Jerature of the liquid, means for conveying said Wet coating onsaid wet paper into contact with said heated surface over an arcuatecasting zone of said drum surface, backing means in contact with thepaper on a side opposite to said coated side for receiving vapor fromsaid coating, a pressure member disposed against said backing means atsaid casting zone for applying pressure to said backing means urging thelatter towards said drum surface, said pressure member being wrappedaround said heated surface through a substantial circumferential arc ofsaid drum and exerting pressure uniformly over said are in excess of themagnitude of the vapor pressure of the boiling liquid minus the pressureloss due to the passage of vaporized liquid through the coating and thepaper until the cohesive strength of the coating will resist anydistortion due to further drying.

10, Apparatus for casting a Wet coating on a paper wherein the coatingincludes solids and a liquid comprising: a rotatable casting drum havinga smooth polished surface heated to a temperature in excess of theboiling temperature of the liquid, means for conveying said Wet coatingon said paper into contact with said heated surface over an arcuatecasting zone of said drtun surface, backing means in contact with thepaper on a side opposite to said coated side for receiving vapor fro-msaid coating, a pressure member disposed against said backing means atsaid "casting zone for applying pressure to said backing means urgingthe latter towards said drum surface, said pressure member comprising aflexible continuous belt in contact with said backing means, saidpressure member being wrapped around said heated surface through asubstantial circumferential are of said drum and exerting pressureuniformly over said are in excess of the magnitude of the vapor pressureof the boiling liquid minus the pressure loss due to the passage ofvaporized liquid through the coating and the paper until the cohesivestrength of the coating will resist any distortion due to furtherdrying.

11. The method of cast coating paper and the like comprising coating apaper sunface with a hardenable liquid coating containing a pigment andan adhesive in a volatile liquid, heating a smooth polished drum surfaceto a temperature above the boiling temperature of the liquid, applying acontinuous vapor receiving and absorbing backing layer into continuouscontact with said paper, pressing a continuous belt against said backinglayer forcing said coating into continuous contact With and around asubstantial portion of said drum surface at a pressure at least equal tothe vapor pressure of the liquid in contact with the drum surface minusthe pressure loss due to the passage orf vaporized liquid through thecoating and the paper.

12. The method of cast coating paper and the like comprising coating apaper surface with a hardenable liquid coating containing a pigment andan adhesive in a volatile liquid, heating a smooth polished drum sunfaceto a temperature above the boiling temperature of the liquid, applying acontinuous vapor receiving and absorbing backing layer into continuouscontact with said paper, pressing a continuous non-porous belt againstsaid backing layer forcing said coating into continuous contact With andaround a substantial portion of said drum surface at a pressure at leastequal to the vapor pressure of the liquid in contact with the drumsurface minus the pressure loss due to the passage of vaporized liquidthrough the coating and the paper.

13. The method of cast coating paper and the like comprising coating apaper Web surface with a hardenable liquid coating containing a volatileliquid and an adhesive which coating is conformable to a smooth formingsurface, pressing :said coated paper surface With a continuousnon-porous pressing surface against a smooth forming surface heated to atemperature sufficient to boil said liquid and under a pressuresuflicient to continuously maintain said coating against said smoothforming surface, maintaining a vapor receiving web between the coatedpaper surface and said pressing surface, continuously maintaining saidpressure for a suflicient time until sufficient volatile liquid has"been vaporized and been driven from the surface of the coating wherebythe cohesive strength of the coating will resist any distortion due tofurther drying.

References Cited in the file of this patent UNITED STATES PATENTS1,944,600 Greene Jan. 23, 1934 2,337,013 Bradner et a1. Dec. 14, 19432,457,433 Barrett Dec. 28, 1948 2,510,313 Houth et al. June 6, 19502,870,038 MacIntyre Jan. 20, 1959 2,919,205 Hant Dec. 29, 1959 FOREIGNPATENTS 393,740 Great Britain Jime 15, 1933

1. THE METHOD OF CAST COATING PAPER AND THE LIKE COMPRISING COATING APAPER WEB SURFACE WITH A HARDENABLE LIQUID COATING CONTAINING A VOLATILELIQUID AND AN ADHESIVE WHICH COATING IS CONFORMABLE TO A SMOOTH FORMINGSURFACE, JPRESSING SAID COATING PAPER SURFACE WITH A CONTINUOUSJPRESSING SURFACE AGAINST A SMOOTH FORMING SURFACE HEATED TO ATEMPERATURE SUFFICIENT TO BOIL SAID LIQUID AND UNDER A PRESSURESUFFICIENT TO CONTINUOUSLY MAINTAIN SAID COATING AGAINST SAID SMOOTHFORMING SURFACE, MAINTAINING A VAPOR RECEIVING WEB BETWEN THE COATEDPAPER SURFACE AND SAID PRESSING SURFACE, CONTINUOUSLY MAINTAINING SAIDPRESSURE FOR A SUFFICIENT TIME UNTIL SUFFICIENT VOLATILE LIQUID HAS BEENVAPORIZED AND BEEN DRIVEN FROM THE SURFACE OF THE COATING WHEREBY THECOHESIVE STRENGTH OF THE COATING WILL RESIST ANY DISTORTION DUE TOFURTHER DRYING.